1. Field of the Invention
This invention relates generally to the field of transmission cables and more particularly to a method and apparatus for waterblocking splices in conductors contained within transmission cables.
2. Description of the Related Art
In marine exploration, an acoustic signal is generated in the water by a seismic source. The signal propagates through the water in the form of a wavefront which encounters the marine subsurface. The wavefront is refracted and part is reflected back from the bottom surface and from substrata towards the water's surface and detected by marine sensors such as hydrophones.
A series of hydrophones usually are encased in a seismic streamer (cable) and towed behind a vessel. The seismic streamer contains insulated electrical wires (conductors) which carry the signals from the hydrophones to seismic recording equipment on the vessel to obtain geophysical information about the substrata. During manufacture of the seismic streamer containing conductors with parallel circuits, two conductive wires are connected (spliced) to form a single wire.
After the completion of a survey, the cable is retrieved from the water and stored on a reel until redeployed for the next survey. The deployment and retrieval operations sometimes cause breaks in the electrical wires within the cable. The break can be repaired by splicing the damaged wires within the cable and then resealing the cable.
When water invades the cable and contacts the conductive wires, the wires short the connection and/or corrode the conductive wires. Areas of the cable that are especially susceptible to water leaks are the areas adjacent to wire splices. Typical insulated wire-to-wire connections in seismic streamers are waterblocked with mastic-filled shrink tubing. Commercially available mastics do not bond to some types of insulation such as polytetrafluoroethylene (PTFE). Therefore, when water invades the area around the splice, the water sometimes seeps through the mastic to the wire.
As disclosed in U.S. Pat. No. 5,183,966, which is incorporated herein by reference, a standard pair of O-rings and shrink tubing can be used to waterblock a splice between two insulated wires. A problem arises, however, when a coupling is required between more than two wires such as joining two parallel circuits to form a single conductor. Constrictive tubing creates a better compression seal around a nearly circular surface than around other shaped surfaces.
A combination of two circular seals creates a figure-8 shape instead of a single, near-circular shape. Shrink tubing the figure-8 configuration, therefore, can leave voids between the seals and the tubing. This creates an area susceptible to water seepage which defeats the purpose of the waterblock.
The present invention addresses the above-noted problem and provides a method and apparatus for waterblocking the area around splices made on multiple conductors.